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          <th colspan="3" align="center">DB-&gt;compact()</th>
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          <td width="20%" align="left"><a accesskey="p" href="dbcreate.html">Prev</a> </td>
          <th width="60%" align="center">Chapter 2. 
                The DB Handle
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    <div class="sect1" lang="en" xml:lang="en">
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          <div>
            <h2 class="title" style="clear: both"><a id="dbcompact"></a>DB-&gt;compact()</h2>
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      <pre class="programlisting">#include &lt;db.h&gt;

int
DB-&gt;compact(DB *db, DB_TXN *txnid,
    DBT *start, DBT *stop, DB_COMPACT *c_data, u_int32_t flags, DBT *end);  </pre>
      <p>
         The <code class="methodname">DB-&gt;compact()</code> method compacts Btree and Recno access method
         databases, and optionally returns unused Btree, Hash or Recno database
         pages to the underlying filesystem.
    </p>
      <p>
         The <code class="methodname">DB-&gt;compact()</code> <span>
            <span>
                  method returns a non-zero error value on failure and 0 on success.
            </span>
            
        </span>
    </p>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="id1632862"></a>Parameters</h3>
            </div>
          </div>
        </div>
        <div class="sect3" lang="en" xml:lang="en">
          <div class="titlepage">
            <div>
              <div>
                <h4 class="title"><a id="id1632429"></a>txnid</h4>
              </div>
            </div>
          </div>
          <p>
                          If the operation is part of an application-specified transaction, the
                          <span class="bold"><strong>txnid</strong></span> parameter is a transaction
                          handle returned from <a class="xref" href="txnbegin.html" title="DB_ENV-&gt;txn_begin()">DB_ENV-&gt;txn_begin()</a>; 
                          if the operation is part of a Berkeley DB Concurrent Data Store group, the
                          <span class="bold"><strong>txnid</strong></span> parameter is a handle returned
                          from <a class="xref" href="envcdsgroup_begin.html" title="DB_ENV-&gt;cdsgroup_begin()">DB_ENV-&gt;cdsgroup_begin()</a>;
                          otherwise NULL.
                      </p>
          <p>
                          If a transaction handle is supplied to this method, then the operation is
                          performed using that transaction. In this event, large sections of the
                          tree may be locked during the course of the transaction.
                      </p>
          <p>
                          If no transaction handle is specified, but the operation occurs
                          in a transactional database, the operation will be implicitly
                          transaction protected using multiple transactions.  These transactions
                          will be periodically committed to avoid locking large sections of the
                          tree.  Any deadlocks encountered cause the compaction operation to
                          be retried from the point of the last transaction commit.
                     </p>
        </div>
        <div class="sect3" lang="en" xml:lang="en">
          <div class="titlepage">
            <div>
              <div>
                <h4 class="title"><a id="id1632702"></a>start</h4>
              </div>
            </div>
          </div>
          <p>
                          If non-NULL, the <span class="bold"><strong>start</strong></span> parameter is
                          the starting point for compaction in a Btree or Recno database. 
                          Compaction will start at the smallest key greater than or equal to the
                          specified key.  If NULL, compaction will start at the beginning of the
                          database.
                     </p>
        </div>
        <div class="sect3" lang="en" xml:lang="en">
          <div class="titlepage">
            <div>
              <div>
                <h4 class="title"><a id="id1632903"></a>stop</h4>
              </div>
            </div>
          </div>
          <p>
                          If non-NULL, the <span class="bold"><strong>stop</strong></span> parameter is
                          the stopping point for compaction in a Btree or Recno database. 
                          Compaction will stop at the page with the smallest key greater than
                          the specified key.  If NULL, compaction will stop at the end of the
                          database.
                     </p>
        </div>
        <div class="sect3" lang="en" xml:lang="en">
          <div class="titlepage">
            <div>
              <div>
                <h4 class="title"><a id="id1632651"></a>c_data</h4>
              </div>
            </div>
          </div>
          <p>
                         
                     </p>
          <p>
                          If non-NULL, the <span class="bold"><strong>c_data</strong></span> parameter
                          contains additional compaction configuration parameters, and returns
                          compaction operation statistics, in a structure of type DB_COMPACT.
                     </p>
          <p>
                          The following input configuration fields are available from the
                          DB_COMPACT structure:
                     </p>
          <div class="itemizedlist">
            <ul type="disc">
              <li>
                <p>
                                <code class="literal">int compact_fillpercent;</code>
                            </p>
                <p>
                                If non-zero, this provides the goal for filling pages, specified as a percentage
                                between 1 and 100.  Any page in a Btree or Recno databases not at or
                                above this percentage full will be considered for compaction.  The
                                default behavior is to consider every page for compaction, regardless
                                of its page fill percentage.
                            </p>
              </li>
              <li>
                <p>
                                <code class="literal">int compact_pages;</code>
                            </p>
                <p>
                                If non-zero, the call will return after the
				specified number of pages have been freed, or
				no more pages can be freed.
                            </p>
              </li>
              <li>
                <p>
                                <code class="literal">db_timeout_t compact_timeout;</code>
                            </p>
                <p>
                                If non-zero, and no <span class="bold"><strong>txnid</strong></span> parameter
                                was specified, this parameter identifies the lock timeout used for implicit transactions, in
                                microseconds.
                            </p>
              </li>
            </ul>
          </div>
          <p>
                        The following output statistics fields are available from the
                        <code class="literal">DB_COMPACT</code> structure:
                    </p>
          <div class="itemizedlist">
            <ul type="disc">
              <li>
                <p>
                                <code class="literal">u_int32_t compact_deadlock;</code>
                            </p>
                <p>
                                An output statistics parameter: if no <span class="bold"><strong>txnid</strong></span> parameter was specified, the number of
                                deadlocks which occurred.
                            </p>
              </li>
              <li>
                <p>
                                <code class="literal">u_int32_t compact_pages_examine;</code>
                            </p>
                <p>
                                An output statistics parameter: the number of database pages reviewed
                                during the compaction phase.
                            </p>
              </li>
              <li>
                <p>
                              <code class="literal">u_int32_t compact_pages_free;</code>
                          </p>
                <p>
                               An output statistics parameter: the number of database pages freed
                               during the compaction phase.
                          </p>
              </li>
              <li>
                <p>
                              <code class="literal">u_int32_t compact_levels;</code>
                          </p>
                <p>
                               An output statistics parameter: the number of levels removed from the
                               Btree or Recno database during the compaction phase.
                          </p>
              </li>
              <li>
                <p>
                              <code class="literal">u_int32_t compact_pages_truncated;</code>
                          </p>
                <p>
                               An output statistics parameter: the number of database pages returned
                               to the filesystem.
                          </p>
              </li>
            </ul>
          </div>
        </div>
        <div class="sect3" lang="en" xml:lang="en">
          <div class="titlepage">
            <div>
              <div>
                <h4 class="title"><a id="id1632483"></a>flags</h4>
              </div>
            </div>
          </div>
          <p>
                          The <span class="bold"><strong>flags</strong></span> parameter must be set to 0
                          or one of the following values:
                     </p>
          <div class="itemizedlist">
            <ul type="disc">
              <li>
                <p><a id="compact_DB_FREELIST_ONLY"></a>
                                 <code class="literal">DB_FREELIST_ONLY</code>
                           </p>
                <p>
                                Do no page compaction, only returning pages to the filesystem that are
                                already free and at the end of the file.  This flag must be set if the
                                database is a Hash access method database.
                           </p>
              </li>
              <li>
                <p><a id="compact_DB_FREE_SPACE"></a>
                                 <code class="literal">DB_FREE_SPACE</code>
                           </p>
                <p>
                                Return pages to the filesystem when possible. If this flag is not
                                specified, pages emptied as a result of compaction will be placed on
                                the free list for re-use, but never returned to the filesystem.
                           </p>
                <p>
                                Note that only pages at the end of a file can be returned to the
                                filesystem.  Because of the one-pass nature of the compaction
                                algorithm, any unemptied page near the end of the file inhibits
                                returning pages to the file system.  A repeated call to the
                                <code class="methodname">DB-&gt;compact()</code> method with a low <span class="bold"><strong>compact_fillpercent</strong></span> may be used to return pages
                                in this case.
                           </p>
              </li>
            </ul>
          </div>
        </div>
        <div class="sect3" lang="en" xml:lang="en">
          <div class="titlepage">
            <div>
              <div>
                <h4 class="title"><a id="id1633063"></a>end</h4>
              </div>
            </div>
          </div>
          <p>
                          If non-NULL, the <span class="bold"><strong>end</strong></span> parameter will
                          be filled in with the database key marking the end of the compaction
                          operation in a Btree or Recno database.  This is generally the first
                          key of the page where the operation stopped.
                     </p>
        </div>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="id1633231"></a>Errors</h3>
            </div>
          </div>
        </div>
        <p>
                         The <code class="methodname">DB-&gt;compact()</code> <span>
            <span>
                 method may fail and return one of the following non-zero errors:
            </span>
            
        </span>
                    </p>
        <div class="sect3" lang="en" xml:lang="en">
          <div class="titlepage">
            <div>
              <div>
                <h4 class="title"><a id="id1632714"></a>DB_LOCK_DEADLOCK</h4>
              </div>
            </div>
          </div>
          <p>
                A transactional database environment operation was selected to resolve
                a deadlock.
            </p>
        </div>
        <div class="sect3" lang="en" xml:lang="en">
          <div class="titlepage">
            <div>
              <div>
                <h4 class="title"><a id="id1633322"></a>DB_LOCK_NOTGRANTED</h4>
              </div>
            </div>
          </div>
          <p>
                A Berkeley DB Concurrent Data Store database environment configured
                for lock timeouts was unable to grant a lock in the allowed time.
            </p>
        </div>
        <div class="sect3" lang="en" xml:lang="en">
          <div class="titlepage">
            <div>
              <div>
                <h4 class="title"><a id="id1633040"></a> DB_REP_HANDLE_DEAD</h4>
              </div>
            </div>
          </div>
          <p>
                When a client synchronizes with the master, it is possible for committed
                transactions to be rolled back. This invalidates all  the database and cursor
                handles opened in the replication environment. Once this occurs, an attempt to use
                such a handle will 
                
                return <code class="literal">DB_REP_HANDLE_DEAD</code>.
                The application will need to discard the handle and open a new one in order to
                continue processing.
            </p>
        </div>
        <div class="sect3" lang="en" xml:lang="en">
          <div class="titlepage">
            <div>
              <div>
                <h4 class="title"><a id="id1633331"></a>DB_REP_LOCKOUT</h4>
              </div>
            </div>
          </div>
          <p>
                The operation was blocked by client/master synchronization.
            </p>
        </div>
        <div class="sect3" lang="en" xml:lang="en">
          <div class="titlepage">
            <div>
              <div>
                <h4 class="title"><a id="id1632885"></a>EACCES</h4>
              </div>
            </div>
          </div>
          <p>
                An attempt was made to modify a read-only database.
            </p>
        </div>
        <div class="sect3" lang="en" xml:lang="en">
          <div class="titlepage">
            <div>
              <div>
                <h4 class="title"><a id="id1633333"></a>EINVAL</h4>
              </div>
            </div>
          </div>
          <p>
                An invalid flag value or parameter was specified.
            </p>
        </div>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="id1633048"></a>Class</h3>
            </div>
          </div>
        </div>
        <p>
                <a class="link" href="db.html" title="Chapter 2.  The DB Handle">DB</a>  
            </p>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="id1632779"></a>See Also</h3>
            </div>
          </div>
        </div>
        <p>
                     <a class="xref" href="db.html#dblist" title="Database and Related Methods">Database and Related Methods</a> 
                </p>
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